1. Field
Apparatuses, devices, and articles of manufacture consistent with the present disclosure relate to quantization and de-quantization of linear predictive coding coefficients, and more particularly, to an apparatus for efficiently quantizing linear predictive coding coefficients with low complexity, a sound encoding apparatus employing the quantizing apparatus, an apparatus for de-quantizing linear predictive coding coefficients, a sound decoding apparatus employing the de-quantizing apparatus, and electronic devices therefor.
2. Description of the Related Art
In systems for encoding a sound, such as voice or audio, Linear Predictive Coding (LPC) coefficients are used to represent a short-time frequency characteristic of the sound. The LPC coefficients are obtained in a pattern of dividing an input sound in frame units and minimizing energy of a predictive error per frame. However, since the LPC coefficients have a large dynamic range and a characteristic of a used LPC filter is very sensitive to quantization errors of the LPC coefficients, the stability of the LPC filter is not guaranteed.
Thus, quantization is performed by converting LPC coefficients to other coefficients easy to check the stability of a filter, advantageous to interpolation, and having a good quantization characteristic. It is mainly preferred that the quantization is performed by converting LPC coefficients to Line Spectral Frequency (LSF) or Immittance Spectral Frequency (ISF) coefficients. In particular, a method of quantizing LPC coefficients may increase a quantization gain by using a high inter-frame correlation of LSF coefficients in a frequency domain and a time domain.
LSF coefficients indicate a frequency characteristic of a short-time sound, and for frames in which a frequency characteristic of an input sound is rapidly changed, LSF coefficients of the frames are also rapidly changed. However, for a quantizer using the high inter-frame correlation of LSF coefficients, since proper prediction cannot be performed for rapidly changed frames, quantization performance of the quantizer decreases.